As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is absent.
Among the methods used to correct for the eye's failure to accommodate are lenses that have more than one optical power. In particular, contact and intraocular lenses have been developed in which zones of distance, near, and intermediate power are provided.
Additionally, it is known that an individual's pupil size varies with age, luminance, and refractive prescription. For example, as luminance increases, pupil size decreases while, as a person ages, the pupil's response to changes in illumination diminishes. For individuals with presbyopia that is corrected with low add power, for example 1.50 diopters of add power or less, the pupil size will be larger than those requiring greater add power. The reason is that, in general, those requiring less add power are younger in age and have larger pupil sizes at a given luminance than does an older individual.
Conventional lenses typically do not account for pupil size and, thus, are less efficient in distributing light to the lens wearer in all viewing conditions. This results in suboptimal vision. Therefore, a need exists for a lens the design of which takes into account pupil size.